Celiac Disease: A malabsorption syndrome that is precipitated by the ingestion of foods containing GLUTEN, such as wheat, rye, and barley. It is characterized by INFLAMMATION of the SMALL INTESTINE, loss of MICROVILLI structure, failed INTESTINAL ABSORPTION, and MALNUTRITION.Glutens: Prolamins in the endosperm of SEEDS from the Triticeae tribe which includes species of WHEAT; BARLEY; and RYE.Gliadin: Simple protein, one of the prolamines, derived from the gluten of wheat, rye, etc. May be separated into 4 discrete electrophoretic fractions. It is the toxic factor associated with CELIAC DISEASE.Diet, Gluten-Free: A diet which is devoid of GLUTENS from WHEAT; BARLEY; RYE; and other wheat-related varieties. The diet is designed to reduce exposure to those proteins in gluten that trigger INFLAMMATION of the small intestinal mucosa in patients with CELIAC DISEASE.Transglutaminases: Transglutaminases catalyze cross-linking of proteins at a GLUTAMINE in one chain with LYSINE in another chain. They include keratinocyte transglutaminase (TGM1 or TGK), tissue transglutaminase (TGM2 or TGC), plasma transglutaminase involved with coagulation (FACTOR XIII and FACTOR XIIIa), hair follicle transglutaminase, and prostate transglutaminase. Although structures differ, they share an active site (YGQCW) and strict CALCIUM dependence.Reticulin: A scleroprotein fibril consisting mostly of type III collagen. Reticulin fibrils are extremely thin, with a diameter of between 0.5 and 2 um. They are involved in maintaining the structural integrity in a variety of organs.Dermatitis Herpetiformis: Rare, chronic, papulo-vesicular disease characterized by an intensely pruritic eruption consisting of various combinations of symmetrical, erythematous, papular, vesicular, or bullous lesions. The disease is strongly associated with the presence of HLA-B8 and HLA-DR3 antigens. A variety of different autoantibodies has been detected in small numbers in patients with dermatitis herpetiformis.Duodenum: The shortest and widest portion of the SMALL INTESTINE adjacent to the PYLORUS of the STOMACH. It is named for having the length equal to about the width of 12 fingers.Immunoglobulin A: Represents 15-20% of the human serum immunoglobulins, mostly as the 4-chain polymer in humans or dimer in other mammals. Secretory IgA (IMMUNOGLOBULIN A, SECRETORY) is the main immunoglobulin in secretions.Jejunum: The middle portion of the SMALL INTESTINE, between DUODENUM and ILEUM. It represents about 2/5 of the remaining portion of the small intestine below duodenum.Intestinal Mucosa: Lining of the INTESTINES, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. In the SMALL INTESTINE, the mucosa is characterized by a series of folds and abundance of absorptive cells (ENTEROCYTES) with MICROVILLI.HLA-DQ Antigens: A group of the D-related HLA antigens found to differ from the DR antigens in genetic locus and therefore inheritance. These antigens are polymorphic glycoproteins comprising alpha and beta chains and are found on lymphoid and other cells, often associated with certain diseases.Biopsy: Removal and pathologic examination of specimens in the form of small pieces of tissue from the living body.Intestine, Small: The portion of the GASTROINTESTINAL TRACT between the PYLORUS of the STOMACH and the ILEOCECAL VALVE of the LARGE INTESTINE. It is divisible into three portions: the DUODENUM, the JEJUNUM, and the ILEUM.Autoantibodies: Antibodies that react with self-antigens (AUTOANTIGENS) of the organism that produced them.Prolamins: A group of seed storage proteins restricted to the POACEAE family. They are rich in GLUTAMINE and PROLINE.Avena sativa: A plant species of the family POACEAE that is widely cultivated for its edible seeds.Interleukin-18 Receptor beta Subunit: A subunit of the interleukin-18 receptor that plays a role in receptor signaling by association of its cytoplasmic domain with SIGNAL TRANSDUCING ADAPTOR PROTEINS such as MYELOID DIFFERENTIATION FACTOR 88.Diet Therapy: By adjusting the quantity and quality of food intake to improve health status of an individual. This term does not include the methods of food intake (NUTRITIONAL SUPPORT).HLA-DR3 Antigen: An HLA-DR antigen which is associated with HLA-DRB1 CHAINS encoded by DRB1*03 alleles.IgA Deficiency: A dysgammaglobulinemia characterized by a deficiency of IMMUNOGLOBULIN A.HLA-DR7 Antigen: A HLA-DR antigen that is associated with HLA-DRB1 CHAINS encoded by DRB1*07 alleles.Atrophy: Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes.Malabsorption Syndromes: General term for a group of MALNUTRITION syndromes caused by failure of normal INTESTINAL ABSORPTION of nutrients.Diet, Protein-Restricted: A diet that contains limited amounts of protein. It is prescribed in some cases to slow the progression of renal failure. (From Segen, Dictionary of Modern Medicine, 1992)Wheat Hypersensitivity: Allergic reaction to wheat that is triggered by the immune system.Serologic Tests: Diagnostic procedures involving immunoglobulin reactions.Lactulose: A synthetic disaccharide used in the treatment of constipation and hepatic encephalopathy. It has also been used in the diagnosis of gastrointestinal disorders. (From Martindale, The Extra Pharmacopoeia, 30th ed, p887)Duodenoscopy: Endoscopic examination, therapy or surgery of the luminal surface of the duodenum.Endoscopy, Gastrointestinal: Endoscopic examination, therapy or surgery of the gastrointestinal tract.Antibodies: Immunoglobulin molecules having a specific amino acid sequence by virtue of which they interact only with the ANTIGEN (or a very similar shape) that induced their synthesis in cells of the lymphoid series (especially PLASMA CELLS).Immunoglobulin G: The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of IgG, for example, IgG1, IgG2A, and IgG2B.Autoimmune Diseases: Disorders that are characterized by the production of antibodies that react with host tissues or immune effector cells that are autoreactive to endogenous peptides.Prevalence: The total number of cases of a given disease in a specified population at a designated time. It is differentiated from INCIDENCE, which refers to the number of new cases in the population at a given time.Lymphoma, T-Cell: A group of heterogeneous lymphoid tumors representing malignant transformations of T-lymphocytes.Steatorrhea: A condition that is characterized by chronic fatty DIARRHEA, a result of abnormal DIGESTION and/or INTESTINAL ABSORPTION of FATS.Duodenitis: Inflammation of the DUODENUM section of the small intestine (INTESTINE, SMALL). Erosive duodenitis may cause bleeding in the UPPER GI TRACT and PEPTIC ULCER.Capsule Endoscopy: Non-invasive, endoscopic imaging by use of VIDEO CAPSULE ENDOSCOPES to perform examination of the gastrointestinal tract, especially the small bowel.Jejunal Neoplasms: Tumors or cancer in the JEJUNUM region of the small intestine (INTESTINE, SMALL).Case-Control Studies: Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.Jejunal Diseases: Pathological development in the JEJUNUM region of the SMALL INTESTINE.Intestinal Neoplasms: Tumors or cancer of the INTESTINES.Enteropathy-Associated T-Cell Lymphoma: A primary peripheral T-cell lymphoma in the gastrointestinal tract, most often in the jejunum, associated with a history of CELIAC DISEASE or other gastrointestinal diseases.Enteritis: Inflammation of any segment of the SMALL INTESTINE.Enzyme-Linked Immunosorbent Assay: An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.Enterocytes: Absorptive cells in the lining of the INTESTINAL MUCOSA. They are differentiated EPITHELIAL CELLS with apical MICROVILLI facing the intestinal lumen. Enterocytes are more abundant in the SMALL INTESTINE than in the LARGE INTESTINE. Their microvilli greatly increase the luminal surface area of the cell by 14- to 40 fold.Intestinal Diseases: Pathological processes in any segment of the INTESTINE from DUODENUM to RECTUM.Colitis, Microscopic: A condition characterized by chronic watery DIARRHEA of unknown origin, a normal COLONOSCOPY but abnormal histopathology on BIOPSY. This syndrome was first described in 1980 by Read and associates. Subtypes include COLLAGENOUS COLITIS and LYMPHOCYTIC COLITIS. Both have similar clinical symptoms and are distinguishable only by histology.Endoscopy, Digestive System: Endoscopic examination, therapy or surgery of the digestive tract.